Offshore drilling moratorium: US cites blowout preventers' weak spot
The Obama administration on Monday cited control systems on subsea blowout preventers as one reason for its offshore drilling moratorium. But more than a year before the BP oil spill, authorities learned that balky control systems were the most common cause of blowout preventer failure.
Before he leaped into a lifeboat in the middle of the night on April 20, Christopher Pleasant tried to trigger a deep-sea safety device to squelch the oil-well blowout and fire raging aboard the Deepwater Horizon drill rig.Skip to next paragraph
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In those last frantic minutes in the rig's central control room, Mr. Pleasant – a subsea superviser for Transocean, the rig's owner – pressed two buttons simultaneously to activate a 450-ton blowout preventer sitting 5,300 feet below the sea surface. If its massive "shear ram" valve closed, it would slice through the drill pipe and stop the torrent of burning gas.
For one fleeting moment, the control panel lights offered a ray of hope – showing the shear ram and other BOP valves apparently closing. Valve indicator lights flicked from green (open) to red (closed), he told federal investigators in May in New Orleans.
Yet something wasn't right. Another set of gauges just above the BOP control panel showed no hydraulic pressure at all – "no flow," he testified. Also, the fire was still burning. So, despite BOP control system lights showing the shear-ram closed, it was not.
"I knew it was time to leave," Pleasant testified.
No one knows yet just why the rig's BOP did not work – or why the device's hydraulic-electric control system gave Pleasant the wrong readings. That mystery won't be solved unless the BOP is pulled off the sea floor months from now. But when the Obama administration on Monday issued a revised offshore drilling moratorium in the Gulf, it cited fresh concerns about the reliability of BOP control systems as one reason for its action.
Indeed, more than a year before Pleasant's frantic efforts to stop an inferno, a large study of BOP reliability in the Gulf of Mexico had warned industry experts and federal safety officials that balky control systems were by far the most common cause of BOP failure – and apparently getting worse.
Altogether, 63 percent of blowout preventer test failures cited in that 2009 study, a joint effort by the industry and the regulatory US Minerals Management Service (MMS), involved control systems. By contrast, a similar study a decade earlier had found control systems were responsible for 51 percent of BOP failures.
Control systems are vulnerable to leaks
Blowout preventer control systems are hydraulic and electrical units housed in two waterproof pods – the electronic brains of the school-bus-size BOP stacks. The pods – one blue, one yellow – are identical systems, each a backup for the other. Hydraulic and electrical conduits run from the rig deck above the ocean's surface to the pods on the sea floor.
But these control systems, many of them newer-generation units activated by microprocessors, are vulnerable to leaks and failures that can render a BOP useless, according to the closely held study, first reported by the Monitor.
Those microprocessor-based, or "multiplex," control systems enable BOPs to respond in an instant to an electrical signal from the rig – a rate much faster in deep water than that of older, hydraulic-only systems. But there is a downside, too.
"These systems are newer within the industry and thus efforts to improve reliability have not been as extensive," the 2009 study found. They "are much more complex, with more subsea components."